Project Summary/Abstract HIV-associated neurocognitive disorders (HAND) persist in virally suppressed patients. HAND is a heterogeneous disease that is characterized by chronic low-level inflammation, excitotoxicity, presence of neurotoxic HIV proteins, altered APP processing, and other factors that aggravate neuronal structure and function. Opioid use is common among HIV+ patients and thought to contribute to HAND, although this remains controversial. Studies from the previous funding period suggest that morphine can augment HAND by altering APP processing through a novel, iron-dependent pathway. Toxic APP cleavage products are known to reduce dendritic spines in several brain areas, which are critical mediators of learning and memory. Surprisingly, the effects of APP cleavage products on dendritic spines of the prefrontal cortex (PFC), which is an area of critical importance to HAND, have not been studied in depth. This project will elucidate the role of altered APP processing in morphine and HIV-induced neuronal deficits in the PCF. Studies will unravel the interaction between HIV and A? proteins and determine whether morphine can contribute to alteration of APP processing and spines in HAND. Research in aim 1 will concentrate on the effect of A? oligomers on dendritic spine structure and function in PFC neurons, in the presence and absence of HIV neurotoxins or morphine. These in vitro and in vivo studies will define meaningful changes in dendritic spine density/morphology/turnover in PFC neurons, and provide a full assessment of exogenously added A? actions in this critical brain area (the role of endogenous A? will be further tested in aim 3). The main goal of aim 2 is to establish the extent to which -opioids can affect amyloidogenesis through modulation of neuronal iron. These mechanistic studies are based on our recent discoveries suggesting a role for iron in morphine-mediated dendritic spine reduction in cortical neurons. They are also supported by the finding that endosome deacidification leads to increase of cytosolic Fe2+ and A?. Importantly, cytosolic Fe2+ regulates APP expression whilst endolysosomal pH modulates protein degradation. In aim 3, we will employ newly generated molecular tools able to shift APP processing to the ?-cleavage pathway or prevent APP cleavage by ?-secretases. After functional testing in primary cultures, the most promising constructs will be expressed in PFC neurons of HAND animal models to determine how effectively they reduce A? levels in the presence of HIV proteins/morphine and if A? reduction contributes to recovery of PFC cognitive tasks. This proposal will shed light on iron-dependent mechanisms of accelerated cognitive decline in HIV+/opiate abusing subjects, which is becoming increasingly relevant as ART- treated patients live longer.